Beware, following compatibility note was added to http://community.bistudio.com/wiki/getPlayerUID:
We are preparing a significant new features in handling the playerId for Operation Arrowhead, significantly improving their security and reliability. However, it is impossible for us to keep the current size limitations for the playerId, and therefore it is important that addon and missions makers adapt their scripts to be able to accept non-numeric (or large numeric) values as well, besides of the small numeric values seen until now. Before implementing and publishing those features we would like to be sure the community content is ready for the change.Note: while for ArmA 2 or ArmA 2: Operation Arrowhead the result always contains a number, it should be always handled as an opaque string. Converting it to a Number can cause precision problems , as Number cannot accurately represent integers above 16777216 (2^24). Moreover, future game versions may provide a non-numeric value as a result.